I have avidly digested all the previous stuff on the forum about wet sumping, but here's my experience, open to suggestions please: Recently bought 1952 A10 plunger, which has been fairly thoroughly gone through: Reground crank, new standard bore, new pistons and rings, new valves, guides, springs. It was rebuilt over the past few years but hasn't been ridden for probably 20. I bought it knowing it had an ongoing problem, so when I first ran it I took out the drain plug (SRM), out came just under a pint of oil. Replaced drain plug, checked everything, it fired second kick, sounds lovely, oil returning strong into oiltank, after about 30-45 seconds starts smoking from both pipes (quite a LOT of smoke) until engines splutters to a halt with oiled plugs. Undo drain plug, out comes another pint of oil. Remove sump plate, observe that oil is dribbling from scavenge pipe, poke up scavenge pipe....dribble stops. Left it for two days and the fresh tray had caught at the most a couple of tablespoons full. Replace sump, prime, kick, starts and runs clean for a minute or two then starts smoking again. Stop engine, remove drain plug, out comes another pint! So I haven't fixed it, but could it still be the scavenge pipe? Or the other non return valve? Or the pump? All suggestions gratefully received. I can't take it out for a decent run cos it's not road registered yet.